/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * A multiset which forwards all its method calls to another multiset. Subclasses should override
 * one or more methods to modify the behavior of the backing multiset as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>
 * <b>Warning:</b> The methods of {@code ForwardingMultiset} forward <b>indiscriminately</b> to the
 * methods of the delegate. For example, overriding {@link #add(Object, int)} alone <b>will not</b>
 * change the behavior of {@link #add(Object)}, which can lead to unexpected behavior. In this case,
 * you should override {@code add(Object)} as well, either providing your own implementation, or
 * delegating to the provided {@code standardAdd} method.
 *
 * <p>
 * <b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingMultiset}.
 *
 * <p>
 * The {@code standard} methods and any collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingMultiset<E> extends ForwardingCollection<E> implements Multiset<E> {

    /** Constructor for use by subclasses. */
    protected ForwardingMultiset() {}

    @Override
    protected abstract Multiset<E> delegate();

    @Override
    public int count(Object element) {
        return delegate().count(element);
    }

    @CanIgnoreReturnValue
    @Override
    public int add(E element, int occurrences) {
        return delegate().add(element, occurrences);
    }

    @CanIgnoreReturnValue
    @Override
    public int remove(Object element, int occurrences) {
        return delegate().remove(element, occurrences);
    }

    @Override
    public Set<E> elementSet() {
        return delegate().elementSet();
    }

    @Override
    public Set<Entry<E>> entrySet() {
        return delegate().entrySet();
    }

    @Override
    public boolean equals(@Nullable Object object) {
        return object == this || delegate().equals(object);
    }

    @Override
    public int hashCode() {
        return delegate().hashCode();
    }

    @CanIgnoreReturnValue
    @Override
    public int setCount(E element, int count) {
        return delegate().setCount(element, count);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean setCount(E element, int oldCount, int newCount) {
        return delegate().setCount(element, oldCount, newCount);
    }

    /**
     * A sensible definition of {@link #contains} in terms of {@link #count}. If you override
     * {@link #count}, you may wish to override {@link #contains} to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    protected boolean standardContains(@Nullable Object object) {
        return count(object) > 0;
    }

    /**
     * A sensible definition of {@link #clear} in terms of the {@code iterator} method of
     * {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #clear}
     * to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    protected void standardClear() {
        Iterators.clear(entrySet().iterator());
    }

    /**
     * A sensible, albeit inefficient, definition of {@link #count} in terms of {@link #entrySet}.
     * If you override {@link #entrySet}, you may wish to override {@link #count} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    @Beta
    protected int standardCount(@Nullable Object object) {
        for (Entry<?> entry : this.entrySet()) {
            if (Objects.equal(entry.getElement(), object)) {
                return entry.getCount();
            }
        }
        return 0;
    }

    /**
     * A sensible definition of {@link #add(Object)} in terms of {@link #add(Object, int)}. If you
     * override {@link #add(Object, int)}, you may wish to override {@link #add(Object)} to forward
     * to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardAdd(E element) {
        add(element, 1);
        return true;
    }

    /**
     * A sensible definition of {@link #addAll(Collection)} in terms of {@link #add(Object)} and
     * {@link #add(Object, int)}. If you override either of these methods, you may wish to override
     * {@link #addAll(Collection)} to forward to this implementation.
     *
     * @since 7.0
     */
    @Beta
    @Override
    protected boolean standardAddAll(Collection<? extends E> elementsToAdd) {
        return Multisets.addAllImpl(this, elementsToAdd);
    }

    /**
     * A sensible definition of {@link #remove(Object)} in terms of {@link #remove(Object, int)}. If
     * you override {@link #remove(Object, int)}, you may wish to override {@link #remove(Object)}
     * to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    protected boolean standardRemove(Object element) {
        return remove(element, 1) > 0;
    }

    /**
     * A sensible definition of {@link #removeAll} in terms of the {@code
     * removeAll} method of {@link #elementSet}. If you override {@link #elementSet}, you may wish
     * to override {@link #removeAll} to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    protected boolean standardRemoveAll(Collection<?> elementsToRemove) {
        return Multisets.removeAllImpl(this, elementsToRemove);
    }

    /**
     * A sensible definition of {@link #retainAll} in terms of the {@code
     * retainAll} method of {@link #elementSet}. If you override {@link #elementSet}, you may wish
     * to override {@link #retainAll} to forward to this implementation.
     *
     * @since 7.0
     */
    @Override
    protected boolean standardRetainAll(Collection<?> elementsToRetain) {
        return Multisets.retainAllImpl(this, elementsToRetain);
    }

    /**
     * A sensible definition of {@link #setCount(Object, int)} in terms of {@link #count(Object)},
     * {@link #add(Object, int)}, and {@link #remove(Object, int)}. {@link #entrySet()}. If you
     * override any of these methods, you may wish to override {@link #setCount(Object, int)} to
     * forward to this implementation.
     *
     * @since 7.0
     */
    protected int standardSetCount(E element, int count) {
        return Multisets.setCountImpl(this, element, count);
    }

    /**
     * A sensible definition of {@link #setCount(Object, int, int)} in terms of
     * {@link #count(Object)} and {@link #setCount(Object, int)}. If you override either of these
     * methods, you may wish to override {@link #setCount(Object, int, int)} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    protected boolean standardSetCount(E element, int oldCount, int newCount) {
        return Multisets.setCountImpl(this, element, oldCount, newCount);
    }

    /**
     * A sensible implementation of {@link Multiset#elementSet} in terms of the following methods:
     * {@link ForwardingMultiset#clear}, {@link ForwardingMultiset#contains},
     * {@link ForwardingMultiset#containsAll}, {@link ForwardingMultiset#count},
     * {@link ForwardingMultiset#isEmpty}, the {@link Set#size} and {@link Set#iterator} methods of
     * {@link ForwardingMultiset#entrySet}, and {@link ForwardingMultiset#remove(Object, int)}. In
     * many situations, you may wish to override {@link ForwardingMultiset#elementSet} to forward to
     * this implementation or a subclass thereof.
     *
     * @since 10.0
     */
    @Beta
    protected class StandardElementSet extends Multisets.ElementSet<E> {
        /** Constructor for use by subclasses. */
        public StandardElementSet() {}

        @Override
        Multiset<E> multiset() {
            return ForwardingMultiset.this;
        }
    }

    /**
     * A sensible definition of {@link #iterator} in terms of {@link #entrySet} and
     * {@link #remove(Object)}. If you override either of these methods, you may wish to override
     * {@link #iterator} to forward to this implementation.
     *
     * @since 7.0
     */
    protected Iterator<E> standardIterator() {
        return Multisets.iteratorImpl(this);
    }

    /**
     * A sensible, albeit inefficient, definition of {@link #size} in terms of {@link #entrySet}. If
     * you override {@link #entrySet}, you may wish to override {@link #size} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    protected int standardSize() {
        return Multisets.sizeImpl(this);
    }

    /**
     * A sensible, albeit inefficient, definition of {@link #equals} in terms of
     * {@code entrySet().size()} and {@link #count}. If you override either of these methods, you
     * may wish to override {@link #equals} to forward to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardEquals(@Nullable Object object) {
        return Multisets.equalsImpl(this, object);
    }

    /**
     * A sensible definition of {@link #hashCode} as {@code entrySet().hashCode()} . If you override
     * {@link #entrySet}, you may wish to override {@link #hashCode} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    protected int standardHashCode() {
        return entrySet().hashCode();
    }

    /**
     * A sensible definition of {@link #toString} as {@code entrySet().toString()} . If you override
     * {@link #entrySet}, you may wish to override {@link #toString} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    @Override
    protected String standardToString() {
        return entrySet().toString();
    }
}
